CVE-2026-9138 in Langflow OSS
Summary
by MITRE • 09/04/2026
IBM Langflow OSS 1.0.0 through 1.11.2 Langflow could allow an authenticated attacker to write arbitrary files to the server due to improper input validation in the SaveToFileComponent. The application constructs local file paths using attacker‑controlled input without sufficient sanitization when handling requests to the /api/v1/run/{flow_id} endpoint. An attacker with low‑privileged authenticated access (such as a valid API key or user session) can supply crafted path values, including absolute paths or path traversal sequences, allowing arbitrary file writes to locations writable by the Langflow process. Successful exploitation may lead to unauthorized file creation or modification, potentially resulting in further compromise depending on the deployment environment.
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Analysis
by VulDB Data Team • 09/04/2026
The vulnerability identified in IBM Langflow versions 1.0.0 through 1.11.2 represents a critical security flaw rooted in improper input validation within the SaveToFileComponent. This component is responsible for handling file operations, specifically when users or automated processes request to save data via the /api/v1/run/{flow_id} endpoint. The core technical failure lies in how the application constructs local file paths using user-supplied inputs without implementing adequate sanitization mechanisms. By failing to restrict or validate the format of these path values, the software allows an attacker to inject absolute paths or directory traversal sequences such as ../ into the request parameters. This lack of validation enables the manipulation of the intended destination for file writes, bypassing expected sandboxing or isolation boundaries that should prevent access outside designated directories.
An attacker with low-privileged authenticated access can exploit this flaw by crafting specific HTTP requests to the vulnerable endpoint. Authentication in this context is defined broadly and includes possession of a valid API key or an active user session, which are common requirements for interacting with Langflow's application programming interface. Once authenticated, the adversary supplies crafted path values that include maliciously constructed file paths. Because the server processes these inputs directly into its file system operations without sufficient checks against directory traversal patterns, it writes files to arbitrary locations on the host machine where the Langflow process has write permissions. This capability effectively grants the attacker control over specific file creation and modification actions within the constraints of the operating system user running the application.
The operational impact of this vulnerability extends beyond simple unauthorized file creation. Depending on the deployment environment, writing arbitrary files can serve as a stepping stone for more severe compromises. For instance, if an attacker can write to configuration directories or script execution paths, they may achieve remote code execution by overwriting critical system files or injecting malicious scripts that are subsequently executed by higher-privileged processes. Even without immediate privilege escalation, the ability to modify application data or logs can lead to integrity violations and potential denial of service conditions. The severity is further amplified in containerized environments where shared volumes might expose sensitive host data if the path traversal allows access beyond the intended container boundaries.
This vulnerability aligns with Common Weakness Enumeration (CWE) categories such as CWE-22, which describes Improper Limitation of a Pathname to a Restricted Directory, commonly known as directory traversal. It also relates to CWE-434, concerning Unrestricted Upload of File with Dangerous Type, although the primary vector here is path manipulation rather than file type filtering. From an adversary perspective, this behavior maps to MITRE ATT&CK techniques involving Command and Scripting Interpreter or System Information Discovery if used for reconnaissance, but primarily falls under Defense Evasion via Obfuscated Files or Hidden Files when used to plant malicious artifacts. The exploitation requires authentication, which places it in the category of authenticated attacks rather than unauthenticated remote code execution vectors.
Mitigation strategies should focus on both immediate remediation and long-term architectural improvements. Users running affected versions must upgrade to a patched version of IBM Langflow where this input validation issue has been resolved by the vendor. In environments where upgrading is not immediately feasible, network-level controls such as web application firewalls can be configured to detect and block requests containing path traversal sequences or absolute paths in API parameters. Additionally, implementing strict file system permissions for the user account running the Langflow process will limit the blast radius of any successful exploitation by restricting write access only to necessary directories. Application developers should also adopt secure coding practices that enforce allow-listing of valid characters for filenames and utilize canonicalization functions to resolve path components before performing file operations, ensuring that all paths remain within an approved base directory.